Minitalk

A C client/server communication project that transfers text using Unix signals. The client encodes a message as individual bits, and the server reconstructs and prints it. Developed as part of the 42 curriculum to practice inter-process communication, signal handlers, and synchronization.

Build

Requirements: a C compiler, Make, Git, and a Unix-like environment with POSIX signals. The project uses the author's libft repository as a pinned submodule.

git clone --recurse-submodules https://github.com/civanaban2/minitalk.git
cd minitalk
make

For an existing clone without initialized submodules:

git submodule update --init --recursive
make

Outputs:

• build/server
• build/client

The Makefile first builds libft/libft.a, then links the client and server. It compiles the project sources with -Wall -Wextra -Werror.

Usage

Start the server in one terminal:

./build/server
# Server PID: 12345

In another terminal, pass the actual PID printed by your running server:

./build/client 12345 "Hello from the client"
# Message sent

The server prints the received text followed by a newline. Quote messages containing spaces. The server stays running for subsequent messages; stop it with Ctrl+C. Use one client at a time and wait for its completion before starting the next.

The example PID is illustrative, not a fixed value. Do not use zero, negative, stale, or unrelated process IDs. The current argument checks are incomplete; use only the PID of the intended server.

Protocol

Client                           Server
  | --- initial signal --------> |
  | <------ acknowledgment ----- |
  | --- 32 message-length bits ->|
  | <--- acknowledgment per bit -|
  | --- 8 bits per text byte --->|
  | <--- acknowledgment per bit -|
  |                              | reconstruct and print

• SIGUSR1 represents a set bit; SIGUSR2 represents a cleared bit.
• Length and character bits are sent least-significant bit first.
• sigaction() with SA_SIGINFO provides the sender PID.
• The length header lets the server allocate its message buffer before payload reception.
• The client uses acknowledgments to pace its signal transmission and waits with pause() between signals.
• Server-side idle handling resets transfer state after approximately one second without an interrupting signal.

This is a byte-oriented text protocol, not a socket or network service. Shell arguments cannot contain embedded NUL bytes, so it is not a general binary-file transfer interface. UTF-8 text is transmitted as bytes rather than decoded as Unicode characters by the program.

Build targets

Command	Action
make	Build both executables and the libft dependency
make clean	Remove project objects and run fclean in libft
make fclean	Also remove the build/ directory
make re	Clean and rebuild; use without parallel -j execution

libft is pinned by the parent repository's gitlink. Initializing the submodule checks out that recorded revision; it does not automatically select the newest libft commit. This documentation update does not change that link.

Structure

Makefile
.gitmodules
inc/minitalk.h       # Shared transfer-state structure
src/client.c        # Handshake, bit encoding and acknowledgments
src/server.c        # Message reconstruction and output
libft/              # Git submodule

Scope and limitations

This is an educational single-client protocol, not a robust IPC library. Multiple simultaneous clients are not supported. PID validation, signal-call error handling, empty-message behavior, signal-mask initialization, and handler async-signal safety need further review. A missing or unresponsive server can leave the client waiting indefinitely.

The implementation assumes a 32-bit length header and uses platform-specific integer typedefs. Portability to every POSIX environment is not guaranteed. These are notes about the existing code, not changes to its behavior.

License

MIT. See LICENSE. The libft submodule retains its own repository history and files.